The present invention relates to novel copolyester compositions and novel methods employing such compositions. The copolyester compositions of the present invention contain a low polarity block segment in the polymer backbone. These copolyester compositions are particularly suitable for use as adhesive and coating materials and exhibit high initial adhesion and superior retained adhesion to various substrates.
Many amorphous copolyester compositions are commonly used as adhesive and coating materials because of their useful properties, which include: strong cohesion when below their glass transition temperatures (xe2x80x9cTgxe2x80x9d), strong adhesion and good clarity. Such compositions are also generally inexpensive. However, amorphous compositions are not suitable in a variety of adhesive and coating applications. For example, such compositions do not adequately adhere to substrates such as polypropylene, polyethylene, thermoplastic polyolefins (xe2x80x9cTPO""sxe2x80x9d) and various other low surface energy substrates. Additionally, the mechanical and adhesive properties of many amorphous adhesives and coatings are often inadequate for certain higher temperature applications above their Tg""s. They also possess limited tensile strength and hydrolytic stability above their Tg. Still further, these materials are generally limited in solvent and chemical resistance.
Crystalline copolyesters are generally superior to amorphous materials, especially when the materials are above their glass transition temperatures, in that they possess many valuable properties, including rigidity, hardness, toughness, tensile strength, abrasion resistance, solvent resistance, chemical resistance, good elevated temperature performance up to their crystalline melt point, good balance of flexibility and toughness, and better hydrolytic stability. However, the adhesion of crystalline polymers to a variety of substrates, such as polyethyleneterephthalate (PET), decreases rapidly over time as these polymers shrink during crystallization and subsequently pull away from the substrate to which they were adhered. Amorphous polymers do not suffer this same fate since shrinkage of these polymers is not significant enough to result in loss of adhesion as they age.
It would, thus, be desirable to provide improved copolyester adhesives and coatings that possess both the properties of amorphous polymers, namely retained adhesion over time (xe2x80x9caged adhesionxe2x80x9d), and the properties of crystalline polymers, namely toughness and tensile strength over a broad temperature range, and superior solvent resistance and hydrolytic stability.
Crystalline copolyester compositions containing a low polarity block in the polymer backbone have been described in various patents. However, these compositions have been developed and used specifically for applications in which their low or anti-adhesion properties are required. Namely, these crystalline copolyester compositions were developed and used to specifically provide slip, for example, in mold forming materials for use in processes wherein the molded articles must be readily released from the mold""s surface.
U.S. Pat. Nos. 4,348,510 and 4,496,704 describe copolyester compositions formed from: hydroxyl terminated polyalkyleneoxide (A) and polydimethylsiloxane (B), in ABA triblock segments copolymerized with polyester forming components. Films, tapes, sheeting and other extruded or molded articles prepared from these polysiloxane block copolyesters are shown to exhibit improved slip or nonblocking tendencies, i.e. reduced tendency to adhere to other materials, as evidenced by their reduced static and kinetic coefficients of friction.
U.S. Pat. No. 4,382,131 and U.S. Pat. No. 4,686,262 describe a polyolefin block copolyester used in producing moldings exhibiting extremely low deformation and distortion even when processed into thin articles, and at the same time, retain their crystallinity despite the addition of the low polarity segment in the copolyester composition. U.S. Pat. Nos. 4,207,230 and 4,223,106 also describe block copolyesters containing a low polarity polyolefin block segment that are used as molding materials with properties being similar to those described in U.S. Pat. No. 4,382,131.
U.S. Pat. No. 3,935,154 describes solvent soluble block copolyester, containing low polarity polysiloxane block segments, suitable for uses which require good release properties. Specifically, the compositions described are particularly useful in the photographic field as release agents for photoconductive materials.
U.S. Pat. No. 4,659,786 describes a polyester-polysiloxane block copolymer suitable for use as dental impression materials, as well as mold materials for general uses with good release properties. Sealing materials are also claimed.
U.S. Pat. No. 4,927,895 describes a polysiloxane block copolyester that exhibits good resistance to impact shock and to hydrolysis without any loss of the inherent advantageous properties, such as mechanical strength, of the base polyester resin.
U.S. Pat. Nos. 4,845,158 and 4,994,526 describe compositions used to prepare block resins which are molded into gaskets, washers, flexible tubing and similar articles.
U.S. Pat. No. 5,773,517 describes thermoplastic polyolefin block copolyesters that are used as polymer compatibilizers and quality improving agents. These block copolyesters are blended with and are used to improve various properties of other polymers, such as impact strength, tensile strength; elongation, heat resistance, paintability, weather resistance, elasticity, resilience, flowability, dimensional stability and chemical resistance.
It would thus be desirable to provide improved copolyester adhesive and coating materials that possess both advantageous properties of amorphous polymers, specifically improved and/or retained adhesion over time, and advantageous properties of crystalline polymers, especially superior hydrolytic stability, solvent resistance, chemical resistance, tensile strength and toughness over a broad temperature range.
It has now been discovered that copolyesters containing low polarity segments in their backbone possess unexpected properties that make them particularly useful as adhesive and coating materials.
The present invention provides high performance block copolyester compositions that are particularly suitable for use as adhesives and coatings because these materials incorporate the advantages of crystalline polymers while possessing the quality of retained or aged adhesion of amorphous polymers.
The compositions of the present invention comprise a copolyester having a low polarity block segment incorporated into the copolyester backbone. These compositions are superior in initial adhesion and aged adhesion, and they retain toughness and resistance to solvents while possessing improved wettability and hydrolytic stability over a broad temperature range.
The copolyesters of the present invention may be prepared by any conventional method. Preferably, the copolyesters are prepared by standard polycondensation processes utilizing difunctional alcohols and dicarboxylic acids and optionally up to about 3% of a polyfunctional branching agent. This synthesis normally occurs in two stages, with the first stage being a direct esterification or transesterification (alcohololysis) stage and the second stage being a polyesterification stage. See, e.g. V. V. Korshak and S. V. Vinogradova, Polyesters, Chapter III, pp. 72-150, Pergamon Press, N.Y., N.Y., (1965).
The low polarity block is incorporated into the backbone of the copolyester, preferably by its addition at the beginning of the direct esterification 1st stage reaction along with the difunctional alcohols and dicarboxylic acids. The low polarity block may also be added at any time during the direct esterification stage, but preferably prior to the 2nd stage (polyesterification).
Some examples of difunctional alcohols useful in the practice of the present invention include: alkyl diols from C2 to C12, such as ethylene glycol, diethylene glycol, butanediol, propanediol, hexanediol, and the like; cycloaliphatic diols, such as cyclohexanedimethanol and the like; aliphatic diols containing aromatic moieties; and polymeric and/or oligomeric alkyleneoxide polyols having an alkyl chain length of from C2 to C12 (linear or branched), preferably with the polyol having a number average molecular weight from about 300 to 8000, more preferably from about 1000 to about 5000, and most preferably between about 1000 and 3000. Particularly preferred difunctional alcohols are ethylene glycol and butanediol.
Some examples of difunctional carboxylic acids useful in the practice of the present invention include: aliphatic diacids from C4 to C36, such as adipic acid, azelaic acid, sebacic acid, and the dimer acids; cycloaliphatic diacids, such as cyclohexane dicarboxylic acid and the like; aromatic diacids, such as terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid and the like; and the lower (C1 to C6) alkyl esters of said dicarboxylic acids. Particularly preferred difunctional carboxylic acids are terephthalic acid, sebacic acid and isophthalic acid.
Relatively small amounts of polyfunctional branching agents may be added in order to make the material more polyfunctional. The branching agents can be added at any time during the direct esterification stage. Examples of polyfunctional branching agents useful in the practice of the present invention may include those conventionally used, such as: trimellitic anhydride, pyromellitic dianhydride, trimethylolethane, trimethylolpropane and pentaerythritol.
Examples of low polarity block segments useful in the practice of the present invention include: saturated and unsaturated telechelic polyolefins comprised of monomeric units, from C2 to C18, and possessing functional end-groups, such as hydroxyl, carboxyl, anhydride, acid chloride, oxirane and the like, preferably having a weight average molecular weight from about 500 to 4500, more preferably about 1000 to about 4000, and most preferably about 1800 to about 3500; ABA block copolymers with a weight average molecular weight from about 500 to 10,000, preferably about 1500 to about 6000, more preferably about 1800 to about 3500, wherein B is an alkyl and/or aromatic substituted polysiloxane, and where A is a functionally terminated polyalkyleneoxide with an alkyl chain length of C2 to C6; and fluorine substituted telechelic oligomers and polymers, such as polyesters, acrylics, polyurethanes, polyolefins, polycarbonates, epoxies (e.g., epichlorohydrin-bis-phenol and Novolac(copyright) type polymers), and the like. The above-mentioned polyolefins may include a variety of monomers, for example: ethylene, propylene, butylene, isobutylene, other alkyl substituted olefins, xcex1-olefins, butadiene, and/or copolymers thereof. One preferred polyolefin material is Kraton L-2203 (Shell), which is a hydroxyl-terminated butylene/ethylene copolymer comprising about 50% by weight of butylene and about 50% by weight of ethylene, and having an average MW of about 3,000. One preferred hydroxyl terminated ABA polysiloxane triblock material is CoatOSil 2812 (Witco), which comprises about 40% by weight of polyalkyleneoxide (A) and about 60% by weight of polydimethylsiloxane (B). More specifically, the CoatOSil 2812 comprises about 40% by weight of a 350 molecular weight polypropyleneoxide/ethyleneoxide tipped block (A) and about 60% by weight of a 2000 molecular weight polymethylsiloxane block (B).
Thus, a particularly preferred polycondensation reaction involves a reaction of (1) ethylene glycol and/or butanediol, (2) terephthalic acid and/or sebacic acid and/or isophthalic acid and (3) Kraton -2203 and/or CoatOSil 2812. Optionally, one or more of the polyfunctional branching agents listed above may be added, as discussed above.
The thus formed copolyesters of the present invention, having the incorporated low polarity block, preferably have a weight average molecular weight of from about 5,000 to about 150,000. More preferably, the copolyesters, having the incorporated low polarity block, have a weight average molecular weight of from about 10,000 to about 100,000. Most preferably, the copolyesters have a weight average molecular weight of from about 30,000 to about 90,000. The low polarity block is preferably incorporated into the backbone of the copolyesters at levels of from about 0.5 to about 85 weight percent, more preferably from about 1 to about 50 weight percent, and most preferably from about 2 to about 35 weight percent.
The copolymer compositions of the present invention are particularly useful as adhesives and coatings in a variety of applications, and for a wide variety of substrates, either alone, or used as modifiers with other polymers which have not themselves been modified with a low polarity material. For example, some materials to which the compositions of the present invention exhibit unique adhesive properties include materials such as: untreated polyethyleneterephthalate (PET), polyethylenenaphthalate (PEN), untreated oriented polypropylene (OPP), polyvinyl fluoride (Tedlar(copyright)), nylon, polyirnide, polycarbonate, polystyrene, polymethyl methacrylate (PMMA), polyvinyldiene fluoride (Kynar(copyright)), polyurethanes, and cellulosics.
The copolymer compositions of the present invention may further be used as a tie-layer functioning as an adhesive for the purpose of bonding polymer materials with dissimilar surface energies during coextrusion production of composite films. Substrates such as: PET, PEN, polyolefins, vinyl-type-polymers (Tedlar(copyright), Kynar(copyright), PVC), and the like may be utilized in such procedures.
The copolymer compositions of the present invention are also useful as a coated adhesive sheath on a fiber core. As such, the copolymer compositions are coated on the surface of a fiber (core), preferably by extrusion, and utilized as a sheath adhesive. The adhesive sheath may be reactivated with heat and the intersecting fibers fused.
The copolymer compositions of the present invention are also useful as powder adhesives. In such applications, the copolymer compositions are ground to a desired particle size distribution and applied to a carded mat of fibers, which is then compressed and fused to produce non-woven fabrics. These block copolyesters can also be applied to fabrics and used to bond these fabrics to themselves or other substrates. Similarly, the powdered copolymer compositions can be used as adhesives or coatings on films or foils, in a wide variety of applications. For example, such powdered adhesives can be used to adhere cloth, plastic film, or composite materials to foams, e.g. form seating materials, for automotive interior trim applications.
The copolymer compositions may also be used as web or film adhesives. As a web adhesive, the fast-crystallizing, thermoplastic polymers of the present invention are melt extruded into a xe2x80x9cweb-likexe2x80x9d, fibrous material. This fibrous material may then be applied to fabrics, foams, films, etc. and heat activated to form an adhesive bond which exhibits improved retained adhesion to these materials.
Still further, essentially any utility for an adhesive or coating can obtain improved adhesion by inclusion of the low polarity/copolyester materials of the present invention, either as adhesive or coating material per se, or as an adhesion promoter, added to other adhesive or coating materials. The copolymer compositions can be hot-melt or solvent applied, used alone, or in conjunction with curing or thermosetting components. Suitable curable components include aminoplasts, phenoplasts, epoxy resins, polyisocyanates, silanes, aziridines and the like.
Thus compositions of the present inventions can be applied in a variety of forms for a wide variety of adhesive and coating applications, and provide the ability to obtain the unexpected performance advantages in such applications.